jackson deserialize Map object inside List - json

Question

I have the following JSON in a file
[
{"numberEnrolledPerMonthPerWeek":
{
{"year":"2011","numberEnrolled":0,"weeks":2},
{"year":"2011","numberEnrolled":0,"weeks":3},
{"year":"2011","numberEnrolled":0,"weeks":4},
{"year":"2011","numberEnrolled":0,"weeks":5},
{"year":"2011","numberEnrolled":0,"weeks":6},
{"year":"2011","numberEnrolled":0,"weeks":7},
{"year":"2011","numberEnrolled":0,"weeks":8},
{"year":"2011","numberEnrolled":0,"weeks":9}
}
,"country":"Argentina"
},
]
When I use Jackson to deserialise this into a Java object I get the following error
org.codehaus.jackson.map.JsonMappingException: Can not deserialize instance of java.util.LinkedHashMap out of START_ARRAY token
i am using the following code
ObjectMapper mapper = new ObjectMapper();
List<EnrolledEnrolment> enrolments = mapper.readValue(new File("src/main/resources/data/jsonQueriesTestData1.txt"),
new TypeReference<List<EnrolledEnrolment>>(){});
I have used typeReference for the initial array but do how do I use type Reference for the hashmap inside the object EnrolledEnrolment.
private Map<Integer, Enrolled> numberEnrolledPerMonthPerWeek = new HashMap<Integer,Enrolled>();
The error is thrown when it tries to parse the 2nd Array? Any ideas
Thanks

Answer 1

Hard to tell from the lack of an actual error in the original post, but I encountered an issue when trying to automatically deserialize JSON to an Object where the JSON contain a Map within a List.
I was seeing this error:
com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot construct instance of `java.util.LinkedHashMap` (although at least one Creator exists): no String-argument constructor/factory method to deserialize from String value
I fixed it be adding #JsonDeserialize(converter = JsonToMapConverter.class) to my Map in my POJO.
Where that class looked something like this
public class JsonToMapConverter extends StdConverter<String, Map<String, MyPojo>> {
#Override
public Map<String, MyPojo> convert(String value) {
try {
return JsonUtil.convertJsonToMap(value, String.class, MyPojo.class);
}
catch (Exception e) {
throw new RuntimeException(String.format("Failed to convert String to POJO [%s]", value));
}
}
}
With the utility method looking like
public static <K,V> Map<K,V> convertJsonToMap(String json, Class<K> key, Class<V> value) throws IOException {
JavaType type = mapper.getTypeFactory()
.constructMapLikeType(Map.class, key, value);
return mapper.readValue(json.getBytes(StandardCharsets.UTF_8), type);
}